Answer: Solute size
Step-by-step explanation:
The passive process of filtration promotes the movement of solutes across the barrier. The smaller particles move more easily and the larger particles moves less easily or it can be said that the it needs energy to be transported.
The filtration of the solution having small solutes particles can be passed on from higher concentration to lower without the use of energy.
But the large particles needs more energy to move from one region to another.